Generally speaking, there are two major types of sow ingots sold in the aluminum industry today. The first type is the "traditional" sow ingot and the second type is the "low profile" sow which is gaining wide acceptance within the aluminum industry.
Prior art FIGS. 1A and 1B are illustrations of a traditional sow ingot 10 which typically weighs approximately 1200 pounds and resembles an inverted truncated pyramid. The sow 10 is square in plan view (FIG. 1B), usually has a depth D approximately 1/2 the maximum width W, and is formed by pouring molten ingot metal into a mold 20 having a bottom wall 21 and four sloping side walls 21a-21d defining a mold cavity 23. This ingot shape causes a number of problems, generally related to the manner in which the sow solidifies in the sow mold. Specifically, the shape of mold 20 (FIGS. 1C and 1D) causes the ingot to solidify lastly in the interior center region 12, creating two problems. First, the upper surface 14 of the ingot 10 draws down as the metal solidifies and shrinks. Since the sides 15 solidify first, the outer, upper edges 16 are fixed at a relatively high level 17. The central portion 18 of the upper surface 14 then pulls or draws down during solidification to create an undesirable, deeper central depression on the upper surface.
A second drawback is that once the upper surface solidifies, molten metal is trapped within the interior regions of the ingot. Molten metal has a solubility for hydrogen gas of about 0.20 to 0.50 cubic centimeters per 100 grams of metal depending upon temperature. The hydrogen solubility of the solidified aluminum exterior is almost zero. Consequently, if the interior molten zone is sealed from the external environment by the solidified material, a void 19 will tend to form when the hydrogen is expelled from the solidifying metal. Measurements of 1200 pounds sow ingots of the type depicted in FIGS. 1A and 1B have revealed voids 19 that measure as large as 12.times.12 inches by 2 inches thick. If the gas pressure of the entrapped hydrogen within the void 19 is large enough, the overlying solidified metal may be ruptured and this rupture can cause cracks extending from the void to the ingot upper surface 14. The combination of the depression 18, the cracks (not shown) and the voids 19 can be a severe safety problem since water from rain or other sources may become trapped inside the sow ingot, particularly when the sows are stacked outdoors prior to being transferred to a furnace for re-melting. To avoid charging wet sow ingots into the furnace, the sows are typically stored and dried in an indoor staging area, entailing extra handling.
The sow ingots are typically stacked in a storage location or staging area prior to delivery to a furnace and are usually handled by a fork truck having a pair of fork lifts 25 adapted to engage the recessed edges 22 of the square bottom 24 of the ingot. These recessed edges 22 formed along the four bottom edges of the ingot allow a fork truck to engage the stack from any side for ease of handling and stacking. However, the upper surface depression 18 contributes to instability of a stack of sow ingots since the depressions tend to cause the individual ingots to become off-balance in relation to each other when the bottom surface 24 of an above in-line ingot does not properly contact the upper depressed surface 14 of the adjacent below ingot in the stack.
The newer low profile sow ingots are designed to avoid the formation of a large, entrapped molten interior zone during the solidification process. These sows typically weigh about 1500 to 2000 pounds. The height of these sows is much lower than the traditional sows of FIG. 1A and 1B. Consequently, to cast the same amount of metal in the low profile sow as compared to the sow of FIG. 1A, the base area of the ingot is increased by utilizing a low profile mold having an elongate rectangular base. The low profile sow also includes side "wings" or extensions projecting above the base that promote heat loss and increase the sow ingot volume without increasing depth. In comparison with the prior art sow of FIG. 1A, the low profile sow ingot is a safer product since it reduces chances of water infiltration and stacks better due to the flatter upper surface. However, the presence of internal voids and a slightly depressed upper surface can still exist, albeit to a lesser extent than in the sows of FIG. 1A.
Another major drawback of the previously known low profile sow relates to difficulty in handling. Specifically, a fork lift truck can only pick up such ingot from one of two short sides, limiting access possibilities when storing, when positioning for shipping, or when moving for remelting.
It is accordingly one object of the present invention to provide a low profile sow mold design having enhanced cooling rates and improved solidification characteristics that promotes a solidification front in the sow ingot which moves from the bottom to the top by enhancing heat transfer capability in the bottom.
Another object of the invention is to provide an improved low profile sow ingot and sow mold design therefor preventing or reducing the possibility of initial solidification occurring in the upper surface of the ingot to thereby decrease the potential of internal voids and upper surface depressions in the ingot.
Another object of the invention is to provide a unique sow ingot and sow mold design formed with a unique arrangement of depressions or concavities in the sow ingot bottom that correspond to depressions or concavities in the bottom of the sow mold and are positioned to receive and nest upon a pair of fork lift tines entering the associated depressions or concavities from any of the four sides of the ingot.